1. Field of the Invention
The present invention relates to an electromagnetic fuel injection valve, in which: a valve housing includes: a tubular valve seat member having a valve seat in a front end portion thereof; a magnetic cylindrical body coaxially connected to a rear end portion of the valve seat member; a nonmagnetic cylindrical body coaxially and liquid-tightly welded to a rear end of the magnetic cylindrical body; and a hollow cylindrical stationary core coaxially and liquid-tightly welded to a rear end of the nonmagnetic cylindrical body, a valve assembly is housed in the valve housing and includes: a valve body capable of being seated on the valve seat; and a movable core connected to a rear end of the valve body and opposed to a front end of the stationary core, and a stopper member is provided to the valve housing so as to catch the valve body and thus to restrict an opening stroke of the valve body, wherein each of the valve body and the valve seat member is made of a martensitic stainless steel, and especially relates to an electromagnetic fuel injection valve improved to be suitable for the injection of alcohol fuel.
2. Description of the Related Art
Such an electromagnetic fuel injection valve is known from the Japanese Patent No. 3819741.
Such an electromagnetic fuel injection valve has been developed to be suitable for gasoline fuel injection. However, when used to inject alcohol fuel, this electromagnetic fuel injection valve proves to have a significantly degraded performance. The inventors have found that the degraded performance is attributable to the following.
A valve body and a valve seat member each generally made of a martensitic stainless steel are hardened to a desirable degree by their heat treatment. When the electromagnetic fuel injection valve is used to inject alcohol fuel, adhesive wear occurs in a seat portion where the valve body is seated on the valve seat member under the influence of formic acid and acetic acid existing in the alcohol fuel. As a result, the opening degree between the valve body and the valve seat increases, and the increased opening degree increases the amount of injected fuel. Otherwise, the area of a seat portion between the valve body and the valve seat increases, and this increases an adhering force of the valve body. As a result, the responsiveness of the valve body for its opening operation decreases, and this accordingly decreases the amount of injected fuel.
Against this background, a special material exhibiting a stronger resistance against the alcohol fuel, such as X15NT that is a high-grade martensitic stainless steel, may be selected to form the valve body and the valve seat member. However, such a material is so expensive that the costs for the electromagnetic fuel injection valve considerably increases. For this reason, the choice of such a material is not favorable.